1. Technical Field
The present disclosure relates to a method for manufacturing a semiconductor substrate, a method for manufacturing a semiconductor device, and a semiconductor device. In particular, the disclosure relates to a technique to form a silicon-on-insulator (SOI) structure on a semiconductor substrate.
2. Related Art
The above method for manufacturing a semiconductor substrate forms an SOI layer on a part of a bulk silicon substrate with a separation by bonding Si islands (SBSI) method, and further, an SOI transistor is formed on the SOI layer, as described in T. Sakai et al., Second International SiGe Technology and Device Meeting, Meeting Abstract, pp. 230-231, May (2004). Forming the SOI layer on a part of the bulk silicon substrate makes it possible to form the SOI transistor at a low cost.
A method for forming an SOI structure on a bulk silicon substrate will be described with reference to FIGS. 11A, 11B and FIG. 12. FIG. 11A is a schematic plan view showing a part of a method for manufacturing a semiconductor substrate and FIG. 11B is a schematic sectional view of FIG. 11A. FIG. 12 is a schematic sectional view showing a part of a method for manufacturing a semiconductor substrate. In a case where an SOI structure is formed on a bulk silicon substrate 101, it is conceivable that a local oxidation of silicon (LOCOS) oxide film 104 is formed on the bulk silicon substrate 101 so as to insulate a region for the SOI structure from a region for a bulk structure. As shown in FIG. 11B, for example, the LOCOS oxide film 104 can be formed on the bulk silicon substrate 101 in a manner to surround an SOI region 102 so as to insulate the SOI region 102 for the SOI structure from a bulk region 103 for the bulk structure. Next, silicon-germanium (SiGe) layers 105a and 105b and silicon (Si) layers 106a and 106b are grown epitaxially on the bulk silicon substrate 101 in accordance with the above SBSI method. This process forms a single-crystalline silicon layer 111 (including a first silicon-germanium layer 105a, and a first silicon layer 106a) on a part, corresponding to the SOI region 102, of the bulk silicon substrate 101. The single-crystalline silicon layer 111 succeeds the crystallinity of the bulk silicon substrate 101. At the same time, a polycrystalline silicon layer 112 (including a second silicone-germanium layer 105b and a second silicon layer 106b) is formed on the LOCOS oxide film 104.
Next, a recess 107a (refer to FIG. 11A) is formed so as to form a support 107 for supporting the silicon layer 106a. After an oxide film for forming a support 107 is formed, in order to obtain a form of an element region, a part, which is an exterior region of the element region, of each of the oxide film, the silicon layers 106a and 106b, and the silicon-germanium layers 105a and 105b is dry-etched. Then, the first silicon-germanium layer 105a is selectively etched by hydrofluoric-nitric acid, forming a cavity 108 (refer to FIG. 12) under the first silicon layer 106a which is supported by the support 107. Then, an insulating layer such as SiO2 is implanted into the cavity 108, forming a buried oxide (BOX) layer between the bulk silicon substrate 101 and the silicon layer 106a. After that, a top surface of the bulk silicon substrate 101 is planarized so as to expose the first silicon layer 106a, forming an SOI structure at the SOI region 102 on the bulk silicon substrate 101.
However, in a case (refer to FIG. 11A) where the recess 107a is formed on the LOCOS oxide film 104 (including other oxide films), as shown in FIG. 11B, an end face (a side face) of a polycrystalline silicon layer 112 formed on the LOCOS oxide film 104 is exposed when the support 107 is formed. Therefore, when the first silicon-germanium layer 105a is removed by etching, the polycrystalline silicon layer 112 is exposed to hydrofluoric-nitric acid as well. Polycrystalline silicon has a higher etching rate than single-crystalline silicon, thereby being removed together with the first silicon-germanium layer 105a. Therefore, as shown in FIG. 12, a cavity 108a is formed at the lateral part, which should be remained, of the first silicon layer 106a, so that only an absorption power of an under face 107b of the support 107 supports the first silicon layer 106a. Accordingly, the first silicon layer 106a possibly peels off from the support 107. Peeling off of the first silicon layer 106 makes such a problem that a characteristic of a transistor element having an SOI structure is deteriorated, or the transistor element having an SOI structure can not be formed thereon.